Responses of legumes and grasses to non-, moderate,and dense shade in Missouri, USA. I. Forage yieldand its species-level plasticity
Kejia Pang . J. W. Van Sambeek . Nadia E. Navarrete-Tindall .
Chung-Ho Lin . Shibu Jose . H. E. Garrett
Received: 17 June 2016 / Accepted: 11 January 2017
� Springer Science+Business Media Dordrecht 2017
Abstract Annual screenings of forage grasses and
legumes for shade tolerance were conducted from
1996 to 2001 in the outdoor Shade Tolerance Screen-
ing Laboratory at the Horticulture and Agroforestry
Research Center, University of Missouri. Forty-three
forages were grown under non-shade (100% of full
sunlight), moderate shade (45%), and dense shade
(20%) without competition for water and nutrients.
Annual forage yield (g pot-1) was equal to or higher
under moderate shade for all 43 forages and under
dense shade for 31 forages than the non-shade control.
Relative distance plasticity index (RDPI), a measure
of a species’ adaptability to different environments,
ranged from 0.104 to 0.567. Cool season grasses had
the lowest RDPI (0.183), followed by warm season
grasses (0.252), warm season legumes (0.274), and
cool season legumes (0.314), indicating grasses tend to
be more shade tolerant than legumes in terms of forage
yield. Overall, most grass and legume forages have the
potential to produce equivalent or higher yields in
agroforestry practices featuring light to moderate
shade than forages in open pastures when competition
from tree roots is minimized.
Keywords Shade tolerance � Relative distance
plasticity index � Annual biomass � Warm-season
forages � C4 grasses
Introduction
An agroforestry system, in which trees and forages or
crops are intentionally integrated, has both economic
and ecological benefits including diversifying sources
of income for landowners, mitigating soil erosion,
improving water quality, increasing biodiversity, and
moderating microclimate extremes (Gold and Garrett
2009). The microclimate factors affected include
humidity, soil and air temperature, soil moisture, and
especially, light intensity and quality (Martsolf 1966;
Callaway 2007). Consequently, the yield of forages
grown in agroforestry systems are likely to differ from
forages grown in open fields or pastures (Pearson
1983; Watson et al. 1984). Our knowledge about the
Electronic supplementary material The online version ofthis article (doi:10.1007/s10457-017-0067-8) contains supple-mentary material, which is available to authorized users.
K. Pang (&) � C.-H. Lin � S. Jose � H. E. Garrett
Center for Agroforestry, University of Missouri, 203
Natural Resource Bldg., Columbia, MO 65211-7270,
USA
e-mail: [email protected]
J. W. Van Sambeek
Northern Research Station, USDA Forest Service, 202
Natural Resource Bldg., Columbia, MO 65211-7270,
USA
N. E. Navarrete-Tindall
Cooperative Extension, Lincoln University, 306 Allen
Hall Bldg., 900 Chestnut Street, Jefferson City,
MO 65101, USA
123
Agroforest Syst
DOI 10.1007/s10457-017-0067-8
shade tolerance of forage species is usually qualitative,
i.e., whether they occur in shaded environment, while
quantitatively how adaptive these forages are to
reduced light remains little explored.
Investigations of shade tolerance for forages have
been conducted under a wide range of environmental
conditions, from green shade created by tree canopies
to neutral shade produced by shade cloth or slats under
which the distribution of light wavelengths remain
unchanged. Examples include studies by Peri et al.
(2002) on the photosynthetic response of cocksfoot
(Dactylis glomerata) and white clover (Trifolium
repens) in a silvopastoral setting, by Beard (1965) on
qualitative differences in survival rate and visual
quality of eight turf grass species under tree canopies,
and by Varella et al. (2010) on alfalfa (Medicago
sativa) responses to reduced light under both shade
cloth/slats and tree canopies in agroforestry systems.
Both light intensity and quality (i.e., red: far-red ratio)
under tree canopies can vary depending on species,
canopy density, and duration of sun flecks (Martsolf
1966; Varella et al. 2010), but light intensity under
neutral shade is relatively easy to quantify and light
quality remains unchanged. Researchers have evalu-
ated the shade tolerance of forages using shade cloth
suspended over field-grown plants (Watson et al.
1984; Devkota et al. 1997; Jiang et al. 2004; Ehret
et al. 2015), as well as the shade tolerance of forages
grown in well-watered, enriched potting medium
under shade cloth inside greenhouses (Gaussoin
et al. 1988; Yang et al. 2012; Abraham et al. 2014).
Inside a greenhouse, the full sun treatment can be as
low as 49–67% of the ambient sunlight depending on
the infrastructure and covering (Wong et al. 1985a, b;
Abraham et al. 2014; Albaugh et al. 2014). Using
adequate irrigation, enriched potting medium, and
shade cloth, Lin et al. (1999) evaluated yield responses
of 30 forages grown within a hoop house under
moderate, dense, and non-shade, and Semchenko et al.
(2012) assessed the biomass production of 46 Estonian
grassland species grown under 10, 25, 50, and 100% of
ambient light.
There does not appear to be a clear, concise
definition of shade tolerance or how to measure it
when trying to rank plant species for shade tolerance.
Beard (1965) defined shade tolerance of turf grasses as
the ability to survive and maintain quality. When
ranking multiple species, some species inherently
yield more biomass per plant or unit of occupied area
than others under certain shade levels, thus methods
based on a species’ relative ability to tolerate shade are
required. Wong et al. (1985a) ranked the shade
tolerance of 12 tropical grass forages grown under
each of four shade levels based on the average scores
of several agronomic characteristics. Van Sambeek
et al. (2007) ranked 45 forages based on their
percentage change in forage production under dense
and moderate shade compared to non-shade.
A more comprehensive definition of shade toler-
ance is the capacity of plants to adapt morphologically
and physiologically to maintain productivity under
different light environments (Valladares et al. 2006;
Valladares and Niinemets 2008). These authors pro-
posed calculating the relative distance plasticity index
(RDPI) for traits of plants when grown under at least
three different light environments. Using the RDPI
methodology, we can generate a single value for each
species within each screening trial, thus multiple
RDPIs estimated from multiple trials of different
species can be statistically tested for differences
among species (Valladares et al. 2006).
The objectives of our study were to: (1) assess the
effect of non-, moderate, and dense shade on the
annual cumulative yields of 43 forages grown with
adequate water and nutrients and without root com-
petition from other plants; (2) evaluate whether RDPI
is a useful measure for quantifying shade tolerance.
Materials and methods
Study site
In spring 1996, an outdoor Shade Tolerance Screening
Laboratory (STSL) was constructed at the Horticulture
and Agroforestry Research Center (HARC) in New
Franklin, Missouri (92o 460W, 39o 010N). The STSL
sits on a 0.4 ha pad of limestone gravel laid over
permeable weed barrier for weed control and drainage.
A total of 72 posts (2.5 m tall) were set on a
4.9 9 4.9 m grid and connected by high tensile wires.
Shade cloth made of black polypropylene fabric was
hung over the top of the posts and wires, and along the
sides 0.1 m above the gravel to create nine structures in
a 3 9 3 array (Fig. O1 in Online Resource 1). Each
structure is 14.6 m long (north to south) and 4.9 m
wide, and 4.9 m away from other neighboring struc-
tures. Within each north–south block, three structures
Agroforest Syst
123
were randomly assigned to dense shade (80% shade
cloth, i.e., 20% of full sunlight), moderate shade (55%
shade cloth, 45% of full sunlight), and a non-shade
control (100% of full sunlight). Valves on pro-
grammable timers controlled duration of daily drip
irrigation to each pot. Each structure can hold 20 rows
of six pots on a 0.7 m 9 0.8 m spacing. Pots were
filled with a well-drained potting medium consisting of
composted pine bark, sphagnum peat moss, vermi-
culite, perlite, and sand (15:2:2:5:2 by volume), and
supplemented with slow-release nitrogen (7.9 g N per
10-L pot), micronutrient fertilizer, and a wetting agent.
During the growing season (May through September)
from 1996 to 2001, the study site had an average daily
temperature ranging from 16.6 �C to 27.7 �C. The
minimum and maximum temperature inside the shade
structures were recorded every 4 days from June to
September in 2001. The average minimum tempera-
tures within the non-, moderate, and dense shade
structures were 17.6, 19.2, and 22.2 �C, respectively,
and the average maximums were 35.2, 34.5, and
33.3 �C, respectively. Monthly precipitation during the
same time period averaged 10.7 cm and ranged from
1.9 to 21.7 cm (http://www.ncdc.noaa.gov/cdo-web/
datasets/GHCND/stations/GHCND:USC00236012/
detail). The ambient photosynthetic active radiation
(PAR) in an open field during the growing season
ranged from 36 to 44 mol m-2 day-1 from June to
September (unpublished data).
Plant material
Forages to be evaluated in the newly constructed
STSL were initially selected to replicate the species
screened by Lin et al. (1999). In subsequent years,
forages were selected to repeat screenings of certain
species, and new forages that were part of other on-
going agroforestry studies were also added. Seeds for
our screening trials were obtained from a local farm
supplier, the USDA Elsberry Plant Materials Center,
or harvested from native savanna and prairies in
Missouri. A total of 43 forages (39 species including 2
species having 2 cultivars each and 1 species with 3
cultivars) were chosen for our study (Table 1). These
forages contain annual and perennial, both cool-
season and warm-season, grasses and legumes that
were introduced or are native to the temperate region
of the United States based on information from the
USDA PLANTS database (USDA NRCS 2016).
Seed germination and seedling propagation
Seeds of grass species were germinated in seed starter
flats in a greenhouse in late March or early April each
year except 2001. Seeds of legumes were soaked in
85% rubbing alcohol for 1 min, and rinsed with
deionized water, then placed in petri dishes lined with
wet filter paper. When grass seedlings had one or two
true leaves, or legume seeds had emerging radicles,
three germinants were transplanted to a 442 cm3 pot
filled with a soil medium (Scott’s Metro Mix) until we
had 54 pots for each forage. When the legume
seedlings were established, a commercial rhizobial
inoculum labelled for each species was watered into
the potting medium. Both grasses and legumes were
watered with 0.11 g/L of Peter’s 20-20-20 NPK in the
greenhouse until April or May when six pots of each
cultivar were randomly transplanted into one row of
six black plastic pots (10 L each) in every shade
structure. In 2000, plants after the fall harvest were
overwintered under white plastic film and polyfoam
(Nursery blanket, Hummert Nursery, St. Louis) and
moved back into the structures in spring 2001.
Annual forage yield determination
Forage to a 10-cm stubble height was harvested in
summer at the boot stage (grasses) or early flowering
(legumes) and again in September or October from
1996 through 2000. In 2001, forage was harvested
when the majority of plants within a species started to
boot or flower resulting in up to four harvests. Forage
was oven dried at 70 �C for 72 h to minimize nitrogen
loss. Summer and fall yield of each cultivar within a
structure were summed to determine annual forage
yield (g pot-1) for statistical analysis.
Experimental design and data analysis
Annual yields from 1996 through 1999 were analyzed
using PROC Mixed in SAS 9.4 (SAS Inc., Gary, NC)
for each forage (Eq. O1 in Online Resource 1). Each
analysis is a split plot design with a randomized
complete blocking arrangement for shade (the whole-
plot) and year as the split-plot factor. Shade, year,
shade*year are fixed effects, and block, block*shade,
block*shade*year (residuals) are random effects. A
diagonal covariance structure (type = vc) was
applied. The forages screened in 2000 and 2001 were
Agroforest Syst
123
Table 1 Descriptive characteristics for 43 forages screened from 1996 to 2001 for forage yield under three shade treatments at the
Horticulture and Agroforestry Research Center (HARC), New Franklin, Missouri
Common namea Scientific namea Typeb Originc Lifecycle Years tested
96 97 98 99 00 01
Italian ryegrass Lolium perenne L. subsp. multiflorum
(Lam.) Husnot
CSG I Annual H H H H
Cheatgrass Bromus tectorum L. CSG I Annual H
Clustered fescue Festuca paradoxa Desv. CSG N Perennial H H
Red fescue Festuca rubra L. subsp. rubra CSG N Perennial H H
Kentucky bluegrass Poa pratensis L. CSG Both Perennial H H H
Orchardgrass ‘Benchmark’ Dactylis glomerata L. CSG I Perennial H H H
Perennial ryegrass Lolium perenne L. subsp. perenne CSG I Perennial H H
Redtop Agrostis gigantea Roth CSG I Perennial H H H H
Reed canarygrass Phalaris arundinacea L. CSG N Perennial H H H H
Smooth brome Bromus inermis Leyss. CSG Both Perennial H H H
Timothy Phleum pratense L. CSG I Perennial H H H
Alfalfa ‘Nitro’ Medicago sativa L. CSL I Perennial H H
Alfalfa ‘Victoria’ Medicago sativa L. CSL I Perennial H H
Alsike clover Trifolium hybridum L. CSL I Perennial H H
Crimson clover Trifolium incarnatum L. CSL I Annual H
Crownvetch ‘Penngift’ Securigera varia (L.) Lassen CSL I Perennial H H
Kura clover Trifolium ambiguum M. Bieb. CSL I Perennial H H
Red clover Trifolium pratense L. CSL I Perennial H H H
Sainfoin Onobrychis viciifolia Scop. CSL I Perennial H H
Subterranean clover Trifolium subterraneum L. CSL I Annual H
White clover Trifolium repens L. CSL I Perennial H H H H
Atra paspalum ‘Suerte’ Paspalum atratum Swallen WSG I Perennial H H
Bahiagrass ‘Argentine’ Paspalum notatum Fluegge WSG Both Perennial H H
Bahiagrass ‘Pensacola’ Paspalum notatum Fluegge WSG Both Perennial H H H
Bahiagrass ‘Tifton-9’ Paspalum notatum Fluegge WSG Both Perennial H H H
Bermudagrass Cynodon dactylon (L.) Pers. WSG I Perennial H H H
Eastern gamagrass Tripsacum dactyloides (L.) L. WSG N Perennial H H
Prairie cordgrass Spartina pectinata Bosc ex Link WSG N Perennial H H
Prairie dropseed Sporobolus heterolepis (A. Gray) A.
Gray
WSG N Perennial H H
Rhodes grass ‘Callide’ Chloris gayana Kunth WSG I Perennial H H
Switchgrass ‘Cave-in-rock’ Panicum virgatum L. WSG N Perennial H H H
Bird’s-foot trefoil ‘Norcen’ Lotus corniculatus L. WSL I Perennial H H
Bird’s-foot trefoil
‘rhizomatous’
Lotus corniculatus L. WSL I Perennial H H
Hoary ticktrefoil Desmodium canescens (L.) DC. WSL N Perennial H H H
Illinois bundleflower Desmanthus illinoensis (Michx.)
MacMill. ex B.L. Rob. & Fernald
WSL N Perennial H H H H
Korean clover Kummerowia stipulacea (Maxim.)
Makino
WSL I Annual H
Japanese clover Kummerowia striata (Thunb.) Schindl. WSL I Annual H H
Panicledleaf ticktrefoil Desmodium paniculatum (L.) DC. WSL N Perennial H H H
Purple prairie clover Dalea purpurea Vent. WSL N Perennial H
Agroforest Syst
123
analyzed using an additional autocorrelated covari-
ance structure—AR (1) to address the potential
correlation between first year and the second year
forage yields of the same plants.
Annual yield was also analyzed across years by
grouping forages as the following types: warm season
grasses (WSG, C4), cool season grasses (CSG, C3),
warm season legumes (WSL, C3), or cool season
legumes (CSL, C3), using Eq. O2 (Online Resource 1).
Shade, type, shade*type are fixed effects, species
(type), i.e., species nested in type, and the residuals are
random effects. Annual forage yields were natural-log
transformed before analysis, and then back-trans-
formed for data presentation. Tukey method
(a = 0.05) was applied for the mean separations.
RDPIs were calculated according to Valladares
et al. (2006) as the pairwise comparisons across
replications of annual forage yield under non-, mod-
erate, and dense shade:
RDPI ¼P Xjm�Xj0m0j j
XjmþXj0m0
�
n ð1Þ
where Xjm or Xj0m0 is the forage yield; m or m0 is the
mth block (m or m0 = 1, 2, 3, but m = m0) subjected
to light treatment j or j0 (j or j0 = 1, 2, 3, but j = j0),and n is the total number of all possible pairs of block
and shade treatment in a given year. Missing yield
values of each forage were imputed as the average of
the other two replicates of the same treatment, thus
n = 27. RDPIs were calculated for each cultivar in
each year it was screened. For multiple-cultivar
species, cultivars were treated as replicates, and the
RDPI estimated for that species is the average across
all cultivars and years. To include more forages and
increase the accuracy of estimation, RDPIs were also
calculated from the original data for 27 forages (22
species with 5 species having 2 cultivars each)
screened by Lin et al. (1999) under the same shade
treatments as in this study. RDPIs were natural-log
transformed and compared both among species and
forb types in PROC MIXED, and Tukey method
(a = 0.05) was used for the mean separations.
Results
Annual forage yield
Annual forage yield differed among shade treatments
for 30 of 43 forages (p\ 0.05, Table 2). Year effect
was also significant (p \ 0.05, Table 2) and differ-
ences in yield among years existed for 31 out of the 35
forages screened for more than 1 year (Table O1 in
Online Resource 1). For forages that were tested
between 1996 and 1999, average forage yield across
all shade treatments was generally highest in 1997
(except Rhodes grass ‘Callide’ had higher yield in
1996 than in 1997). No differences in yield were found
among the same forages tested in 1996 and 1998
except Illinois bundle flower with higher yield in 1996
than 1998. Forage yields were equal for 10 forages in
1998 and 1999 with another nine forages yielding less
in 1999 than in 1998. In the two-consecutive-growing-
season trials (2000, 2001), annual forage yields in
2001 of overwintered plants across all shade treat-
ments were higher in 11 out of 13 forages than the
yields of plants started as seedlings in 2000. For the
remaining two forages, alfalfa ‘Nitro’ had equal
Table 1 continued
Common namea Scientific namea Typeb Originc Lifecycle Years tested
96 97 98 99 00 01
Roundhead lespedeza Lespedeza capitata Michx. WSL N Perennial H
Showy ticktrefoil Desmodium canadense (L.) DC. WSL N Perennial H
Slender lespedeza Lespedeza virginica (L.) Britton WSL N Perennial H
Strawberry clover Trifolium fragiferum L. WSL Both Perennial H H H H
a Both common and scientific names followed the information in USDA PLANTS database (USDA NRCS 2016)b CSG cool season grasses (C3), WSG warm season grasses (C4), CSL cool season legumes, WSL warm season legumesc N native to US, I introduced to US
Agroforest Syst
123
Table
2P
rob
abil
ity
of
sig
nifi
can
tF
-val
ue
of
the
fix
edef
fect
sin
the
mix
edef
fect
sm
od
els
for
each
fora
ge,
the
aver
age
ann
ual
fora
ge
yie
ld(g
po
t-1),
and
95
%co
nfi
den
cein
terv
al
(CI)
for
43
fora
ges
gro
wn
un
der
no
n-,
mo
der
ate,
and
den
sesh
ade
bet
wee
n1
99
6an
d2
00
1
Fo
rag
esN
um
ber
of
yea
rste
sted
aF
bN
on
-sh
ade
(fu
llsu
n)
Mo
der
ate
shad
e
(45
%o
ffu
llsu
n)
Den
sesh
ade
(20
%o
ffu
llsu
n)
Sh
ade
(S)
S*
YY
ear
(Y)
Bio
mas
sc
(gp
ot-
1)
95
%C
IB
iom
ass
(gp
ot-
1)
95
%C
IB
iom
ass
(gp
ot-
1)
95
%C
I
Gro
up
1:
45
%=
10
0%
=2
0%
Clu
ster
edfe
scu
e2
,C1
.05
NS
0.0
5N
S1
93
.71
**
*2
2.6
a1
8.2
–2
8.1
24
.9a
20
.1–
30
.92
0.7
a1
6.7
–2
5.7
Eas
tern
gam
agra
ss2
,C1
.15
NS
0.8
7N
S6
8.2
3*
**
26
.6a
18
.3–
38
.73
8.2
a2
6.3
–5
5.6
31
.5a
21
.7–
45
.8
Ch
eatg
rass
11
.63
NS
––
16
.2a
11
.0–
23
.71
5.8
a1
0.8
–2
3.1
11
.0a
7.5
–1
6.1
Ku
racl
ov
er2
,C2
.24
NS
4.5
0N
S1
51
.24
**
*8
.2a
5.3
–1
2.6
7.9
a5
.2–
12
.25
.6a
3.6
–8
.6
Sle
nd
erle
sped
eza
12
.29
NS
––
8.4
a5
.2–
13
.61
1.8
a7
.3–
19
.16
.9a
4.3
–1
1.1
Sh
ow
yti
cktr
efo
il1
3.2
5N
S–
–2
7.4
a1
9.5
–3
8.4
46
.8a
33
.3–
65
.73
3.7
a2
4.0
–4
7.4
Atr
ap
asp
alu
m‘S
uer
te’
23
.32
NS
1.0
0N
S2
3.2
9*
*1
20
.9a
10
5.4
–1
38
.61
36
.2a
11
8.8
–1
56
.21
48
.3a
12
9.4
–1
70
.1
Ro
un
dh
ead
lesp
edez
a1
3.7
5N
S–
–6
.8a
5.2
–9
.09
.9a
7.5
–1
3.1
6.9
a5
.2–
9.1
Sai
nfo
in2
,C3
.94
NS
5.0
7N
S1
21
.10
**
*2
0.0
a1
2.6
–3
1.8
16
.2a
10
.2–
25
.89
.0a
5.7
–1
4.3
Per
enn
ial
ryeg
rass
2,C
4.6
3N
S1
.10
NS
55
.49
**
*2
3.1
a1
4.7
–3
6.4
21
.5a
13
.6–
33
.81
8.3
a1
1.6
–2
8.9
Red
top
45
.57
NS
2.3
4N
S1
7.6
4*
**
43
.2a
34
.8–
53
.65
9.2
a4
7.7
–7
3.4
38
.2a
30
.8–
47
.3
Orc
har
dg
rass
‘Ben
chm
ark
’
35
.83
NS
0.6
7N
S2
7.6
1*
**
34
.1a
30
.4–
38
.34
3.4
a3
8.7
–4
8.7
36
.6a
32
.6–
41
.1
Su
bte
rran
ean
clo
ver
16
.40
NS
––
7.1
a2
.5–
20
.21
1.6
a4
.0–
33
.03
.4a
1.2
–9
.7
Gro
up
2:
45
%[
20
%;
10
0%[
20
%
Bir
d’s
-fo
ot
tref
oil
‘rh
izo
mat
ou
s’
2,C
12
.32
*0
.09
NS
17
4.8
8*
**
44
.6a
33
.5–
59
.35
1.2
a3
8.5
–6
8.2
22
.1b
16
.6–
29
.4
Ko
rean
clo
ver
11
2.1
9*
––
47
.1a
30
.0–
73
.93
7.6
a2
4.0
–5
8.9
16
.2b
10
.3–
25
.4
Illi
no
isb
un
dle
flo
wer
41
4.5
1*
0.9
3N
S1
0.8
0*
**
33
.7a
26
.9–
42
.24
1.4
a3
3.1
–5
1.8
20
.1b
16
.1–
25
.2
Ber
mu
dag
rass
31
7.1
0*
1.4
7N
S3
.08
NS
12
5.3
a1
01
.9–
15
4.1
14
0.1
a1
13
.9–
17
2.4
78
.6b
63
.9–
96
.7
Als
ike
clo
ver
2,C
25
.56
**
6.3
1*
15
.42
**
24
.1a
18
.0–
32
.43
0.2
a2
2.5
–4
0.4
11
.3b
8.4
–1
5.2
Rh
od
esg
rass
‘Cal
lid
e’2
86
.72
**
*1
.06
NS
58
.53
**
*1
01
a8
1.4
–1
25
.39
1.1
a7
3.5
–1
13
57
.1b
46
.0–
70
.8
Jap
anes
ecl
ov
er2
33
.19
**
1.1
8N
S3
4.7
1*
*4
1.2
a3
0.4
–5
5.8
50
.3a
37
.1–
68
.11
3.4
b9
.9–
18
.2
Pu
rple
pra
irie
clo
ver
13
5.2
5*
*–
–8
.0a
5.0
–1
2.7
6.3
a3
.9–
10
.00
.9b
0.6
–1
.4
Red
fesc
ue
2,C
54
.82
**
26
.00
**
11
.01
*3
5.1
a2
6.5
–4
6.3
34
.5a
26
.1–
45
.71
2.7
b9
.6–
16
.8
Pra
irie
cord
gra
ss2
57
.18
**
3.4
9N
S0
.08
NS
35
.1a
24
.8–
49
.83
5.0
a2
4.7
–4
9.6
11
.9b
8.4
–1
6.9
Agroforest Syst
123
Table
2co
nti
nu
ed
Fo
rag
esN
um
ber
of
yea
rste
sted
aF
bN
on
-sh
ade
(fu
llsu
n)
Mo
der
ate
shad
e
(45
%o
ffu
llsu
n)
Den
sesh
ade
(20
%o
ffu
llsu
n)
Sh
ade
(S)
S*
YY
ear
(Y)
Bio
mas
sc
(gp
ot-
1)
95
%C
IB
iom
ass
(gp
ot-
1)
95
%C
IB
iom
ass
(gp
ot-
1)
95
%C
I
Sw
itch
gra
ss‘C
ave-
in-
Ro
ck’
35
7.4
1*
*1
.13
NS
11
.90
**
89
.2a
77
.4–
10
2.8
85
.9a
74
.5–
99
.03
8.5
b3
3.4
–4
4.4
Pra
irie
dro
pse
ed2
,C7
7.8
7*
**
0.0
1N
S4
0.1
6*
**
37
.3a
27
.8–
49
.92
6.0
a1
9.4
–3
4.8
6.0
b4
.5–
8.0
Gro
up
3:
45
%=
10
0%
,1
00
%=
20
%,
45
%[
20
%
Alf
alfa
‘Nit
ro’
2,C
9.0
6*
0.2
4N
S5
.42
NS
45
.2ab
29
.4–
69
.74
8.7
a3
1.6
–7
5.1
18
.5b
12
.0–
28
.5
Alf
alfa
‘Vic
tori
a’2
,C7
.41
*0
.71
NS
13
3.7
8*
**
43
.7ab
30
.2–
63
.15
4.1
a3
7.4
–7
8.1
22
.7b
15
.7–
32
.8
Bir
d’s
-fo
ot
tref
oil
‘No
rcen
’
2,C
7.5
5*
1.4
7N
S1
11
.07
**
*4
1.8
ab2
9.3
–5
9.6
57
.9a
40
.6–
82
.62
4.2
b1
7.0
–3
4.5
Bah
iag
rass
‘Arg
enti
ne’
21
8.8
5*
*1
.22
NS
12
.66
*6
1.8
ab5
3.9
–7
0.9
77
.8a
67
.8–
89
.24
9.7
b4
3.3
–5
7.0
Bah
iag
rass
‘Pen
saco
la’
37
.05
*2
.45
NS
11
.14
**
69
.6ab
55
.1–
87
.88
2.3
a6
5.2
–1
03
.94
8.0
b3
8.0
–6
0.5
Bah
iag
rass
‘Tif
ton
-9’
31
3.7
0*
1.1
5N
S2
.33
NS
71
.5ab
60
.8–
84
.18
6.2
a7
3.3
–1
01
.35
0.8
b4
3.2
–5
9.8
Cri
mso
ncl
ov
er1
10
.56
*–
–1
3.0
ab4
.8–
35
.02
6.5
a9
.8–
71
.24
.3b
1.6
–1
1.5
Red
clo
ver
31
3.6
4*
1.3
8N
S2
1.1
2*
**
36
.7ab
26
.5–
50
.76
2.1
a4
4.9
–8
5.9
21
.3b
15
.4–
29
.4
Tim
oth
y3
8.8
9*
0.8
2N
S2
2.7
3*
**
29
.6ab
20
.3–
43
.34
1.4
a2
8.3
–6
0.6
18
.7b
12
.8–
27
.4
Gro
up
4:
45
%[
10
0%
,1
00
%=
20
%,
45
%[
20
%
Sm
oo
thb
rom
e3
11
.35
*1
.48
NS
68
.26
**
*3
0.6
b2
7.6
–3
3.9
40
.4a
36
.4–
44
.83
1.2
b2
8.1
–3
4.6
Pan
icle
dle
afti
cktr
efo
il3
12
.26
*0
.66
NS
8.0
9*
*4
4.8
b3
5.7
–5
6.1
75
.0a
59
.8–
94
.04
5.4
b3
6.2
–5
6.8
Ital
ian
ryeg
rass
41
7.3
1*
8.8
3*
**
49
.74
**
*3
5.1
b3
0.6
–4
0.3
54
.1a
47
.1–
62
.03
5.7
b3
1.1
–4
0.9
Ken
tuck
yb
lueg
rass
32
3.8
5*
*1
7.7
3*
**
20
3.7
1*
**
19
.1b
16
.9–
21
.63
1.4
a2
7.8
–3
5.5
20
.7b
18
.3–
23
.4
Wh
ite
clo
ver
42
6.5
9*
*4
.55
**
40
.82
**
*2
8.9
b2
2.1
–3
7.8
53
.6a
41
.0–
70
.12
7.3
b2
0.9
–3
5.7
Str
awb
erry
clo
ver
43
1.5
1*
*2
.49
NS
33
.92
**
*2
4.4
b1
8.8
–3
1.6
58
.6a
45
.1–
75
.92
3.1
b1
7.8
–3
0.0
Gro
up
5:
45
%=
20
%,
45
%[
10
0%
,2
0%[
or=
10
0%
Ree
dca
nar
yg
rass
47
.03
*1
.80
NS
8.4
1*
*4
0.5
b3
4.4
–4
7.6
57
.7a
49
.0–
67
.94
7.9
ab4
0.7
–5
6.4
Ho
ary
tick
tref
oil
31
8.8
7*
*1
.51
NS
41
.51
**
*2
5.9
b2
1.7
–3
1.0
48
.6a
40
.6–
58
.13
6.5
ab3
0.5
–4
3.6
Cro
wn
vet
ch‘P
enn
gif
t’2
,C1
3.8
4*
1.5
6N
S1
09
.85
**
*2
8.3
b2
2.9
–3
5.0
37
.9a
30
.7–
46
.83
7.8
a3
0.6
–4
6.7
aC
:co
nse
cuti
vel
yg
row
nfr
om
20
00
to2
00
1b
NS
:n
ot
sig
nifi
can
t(p
C0
.05
);*
0.0
1B
p\
0.0
5;
**
0.0
01B
p\
0.0
1;
***
p\
0.0
00
1c
Mea
ns
wit
hsa
me
des
ign
atio
nle
tter
sw
ith
ina
row
are
no
tsi
gn
ifica
ntl
yd
iffe
ren
t(a
=0
.05
)b
yT
uk
ey’s
test
.V
alu
esw
ere
bac
ktr
ansf
orm
edfr
om
nat
ura
llo
gar
ith
mto
ori
gin
al
scal
e
Agroforest Syst
123
biomass in 2000 and 2001, and alsike clover had
higher biomass in 2000 than in 2001.
Among the 43 forages, five forages showed an
interaction between shade and year (p\ 0.05,
Table 2). Mostly, the interaction occurred due to more
variable yields in the non-shade control (Fig. 1) that
may have been in response to ineffective irrigation
during hot dry weather in some years. Although pots
were automatically irrigated, evidence suggests the soil
surface may have formed a crust so that irrigation water
flowed over the surface without adequately wetting the
soil. Light, long duration precipitation usually elimi-
nated these crusts. Overall, forage yields were the least
during the growing season (May to September) in
1999, which also had the least precipitation: 16 days of
C5 mm and 11 days of C10 mm (Fig. 2) compared to
the average 24.5 and 17.7 days, respectively. The 1999
season also had the second highest number of days
(70 days) with a maximum temperature C30 �C(Fig. 2). The 1998 growing season had the most days
(75) with a maximum temperatureC30 �C; however, it
had more frequent precipitation with 29 days of
C5 mm and 21 days of C10 mm (Fig. 2).
The shade responses of forage yield showed five
major patterns (Table 2). Forages in group 1 showed
no yield differences under all three shade treatments,
indicating these species have a high degree of shade
tolerance. This group included cheat grass, slender
lespedeza, showy ticktrefoil, roundhead lespedeza,
subterranean clover, clustered fescue, eastern gama-
grass, Kura clover, atra paspalum, sainfoin, perennial
ryegrass, redtop, and orchardgrass.
Fig. 1 Annual biomass yield (g pot-1) responses to non-, moderate, and dense shade of the five forages among the 43 forages with
significant interactions (p\ 0.05) between shade and year from 1996 to 2001
Agroforest Syst
123
The forages in group 2 had equal yields between
moderate shade and the non-shade control, but yield
under dense shade averaged 40% of that under
moderate shade and the control. This suggests group
2 is tolerant to moderate, but not dense shade. This
group included bird’s-foot trefoil ‘rhizomatous’, Illi-
nois bundleflower, Bermudagrass, alsike clover,
Rhodes grass, Japanese clover, red fescue, prairie
cordgrass, switchgrass, purple prairie clover, prairie
drop seed, and Korean clover.
In group 3, forage yield was greater under moderate
than under dense shade with no differences between
the control and dense shade nor between the control
and moderate shade. This group, of which the yield
under dense shade averaged 44% of that under
moderate shade, included crimson clover, the two
alfalfa cultivars, bird’s-foot trefoil ‘Norcen’, all 3
bahiagrass cultivars, red clover, and timothy.
In group 4, forages grown under moderate shade
had higher yield than the control or dense shade with
no differences between the latter two treatments.
Yields under the control and dense shade averaged
about 59 and 60% of that under moderate shade,
respectively. Forages in this group included white
clover, strawberry clover, Italian ryegrass, Kentucky
bluegrass, smooth brome, and panicledleaf ticktrefoil.
For group 5, forages under moderate shade grew
better than the control, while plants under dense shade
had biomass growth equal to or exceeding that of the
control. The yield of the forages in the control was
66%, on average, of that under moderate shade, and
77% of dense shade. Forages in this group included
crownvetch, reed canary grass, and hoary ticktrefoil.
A shade effect was detected when grouping forages
by forb types (p\ 0.0001, Table O2 in Online
Resource 1). Although an interaction existed between
forb types and shade treatments (p\ 0.0001), all four
forb types performed best under moderate shade,
followed by the control and dense shade (Fig. 3).
Grasses generally yielded higher biomass than
legumes. Average forage yields declined from warm
season grasses, cool season grasses, and then to warm
season legumes and the cool season legumes as the
two least productive types (p = 0.018).
Relative distance plasticity index
Relative distance plasticity indices for forage yield
ranged from 0.104 to 0.567 for 45 species (Table 3)
with differences existing among species (p\ 0.0001).
The 13 species with the lowest RDPIs and presumably
the most shade tolerant in terms of forage production
Fig. 2 Number of days
with maximum air
temperature C25 or C30 �Cand number of days with
rainfall C5 or C10 mm from
May to September in
1996–2001 in New Franklin,
Missouri
Agroforest Syst
123
were clustered fescue, atra paspalum, crownvetch,
smooth brome, cheatgrass, orchardgrass, roundhead
lespedeza, reed canarygrass, hoary ticktrefoil, bahia-
grass, eastern gamagrass, panicledleaf ticktrefoil, and
perennial ryegrass (Table 3).
Analysis of the four forage types showed that
grasses have lower RDPI than legumes (p\ 0.0001),
with the CSG (C3) having the lowest average RDPI
followed by the WSG (C4), then the WSL (C3), and,
finally, the CSL (C3) having the highest average RDPI
(Table 3).
Discussion
Shade effects on forage yield
Compared to the non-shade control, 34 of the 43
forages showed no differences and nine forages had
greater yields when grown under moderate shade
(Table 2). Likewise, 30 forages showed no differences
and one forage had greater yield than the control when
grown under dense shade (Table 2). In a similar study
by Lin et al. (1999), 13 forages (out of 27) in the two
summer-fall trials, and nine forages in the spring–
summer trial produced no differences between mod-
erate shade and the control, and three forages in the
summer-fall trials had higher yields under moderate
shade than the control. Three forages in the summer-
fall trials and five forages in the spring–summer trial
showed no differences in forage yield between dense
shade and the control. Forages that performed equally
well under moderate shade and the control from both
studies included smooth brome, hoary ticktrefoil,
panicledleaf ticktrefoil, Kentucky bluegrass, orchard-
grass, perennial ryegrass, timothy, and alfalfa ‘Victo-
ria’. Semchenko et al. (2012) discovered that 43 out of
46 temperate grassland species in Estonia grew more
biomass under moderate shade (50% of full sunlight)
than non-shade. These Estonian species include many
grasses, among which some are forages or closely
related to the forages tested in our study, such as soft
brome (Bromus hordeaceus), sweet vernalgrass (An-
thoxanthum odoratum), Kentucky bluegrass, colonial
bentgrass (Agrostis capillaris), creeping bentgrass
(Agrostis stolonifera), orchardgrass, red fescue, tall
fescue (Schedonorus arundinaceus, syn. Festuca
arundinacea in their original text), timothy, and reed
canarygrass.
Similar shade response patterns, i.e., biomass either
plateaued or peaked at moderate shade, have been
found with seedlings of temperate tree species. Loach
(1970) reported that seedlings of five species, both
shade tolerant (Fagus grandifolia and Acer rubrum)
and intolerant (Liriodendron tulipifera, Quercus
rubra, and Populus tremuloides), had comparable or
higher root, stem, and leaf biomass under moderate
shade (44% of full sun) than the control; but biomasses
were lowest under dense shade (17 and 3% of full sun).
Other studies, however, have reported shade
responses that do not plateau or peak at moderate
shade. Devkota (1997) reported a linear increase in
shoot dry weight of ten pasture species across five
shade levels from 14 to 78% of ambient PAR in a
greenhouse study. A similar linear increase was found
in biomass of shade-treated orchardgrass from 10, 30,
to 100% of full sun inside a greenhouse (Abraham
et al. 2014). Both aboveground and belowground
biomass of switchgrass ‘Alamo’ increased when
grown inside a greenhouse as light intensity increased
from 11, to 23, to 31, to 49%, and to 100% of full sun
(Albaugh et al. 2014). Jiang et al. (2004) found
biomass of seashore paspalum (Paspalum vaginatum
Swartz) and hybrid Bermudagrass (Cynodon dactylon
L. 9 C. transvaalensis Burtt Davy) cultivars
increased from 10 to 30%, and then to 100% of full
sun.
Fig. 3 Annual biomass yield (g pot-1) responses to non-,
moderate, and dense shade between 1996 and 2001 by forage
types: CSG cool season grasses, WSG warm season grasses,
WSL warm season legumes, and CSL cool season legumes
Agroforest Syst
123
Table 3 Relative distance plasticity index (RDPI), 95% confidence interval (CI), and rank for annual forage yield (g pot-1) of 45
forage species tested between 1994 and 2001
Species Groupa RDPIb 95% CI Rank Number of cultivarsc
1996–2001 1994–1995
Clustered fescue CSG 0.104df 0.063–0.171 1 1 0
Atra paspalum WSG 0.128abcd 0.078–0.210 2 1 0
Crownvetch CSL 0.134abcd 0.081–0.220 3 1 0
Smooth brome CSG 0.136d 0.102–0.181 4 1* 1
Cheatgrass CSG 0.145abcd 0.088–0.238 5 1 0
Orchardgrass CSG 0.148d 0.117–0.187 6 1* 2
Roundhead lespedeza WSL 0.160abcd 0.079–0.323 7 1 0
Reed canarygrass CSG 0.161bcd 0.114–0.229 8 1 0
Hoary ticktrefoil WSL 0.162cde 0.122–0.216 9 1* 1
Bahiagrass WSG 0.163cd 0.127–0.208 10 3 0
Eastern gamagrass WSG 0.172abcd 0.104–0.282 11 1 0
Panicledleaf ticktrefoil WSL 0.174bcd 0.131–0.232 12 1* 1
Perennial ryegrass CSG 0.175abcd 0.128–0.240 13 1* 1
Showy ticktrefoil WSL 0.189abcd 0.094–0.380 14 1 0
Italian ryegrass CSG 0.194abcd 0.137–0.276 15 1 0
Redtop CSG 0.197abcd 0.139–0.279 16 1 0
Kentucky bluegrass CSG 0.208abcd 0.156–0.277 17 1* 1
Tall fescue CSG 0.226abcd 0.170–0.301 18 0 2
Rhodes grass WSG 0.228abcd 0.139–0.374 19 1 0
Slender lespedeza WSL 0.247abcd 0.150–0.406 20 1* 1
Kura clover CSL 0.249abcd 0.152–0.409 21 1 0
Sericea lespedezad WSL 0.254abcd 0.155–0.418 22 0 1
Timothy CSG 0.257abcd 0.193–0.343 23 1* 1
Bermudagrass WSG 0.263abcd 0.185–0.373 24 1* 1
Illinois bundleflower WSL 0.267abcd 0.188–0.379 25 1 0
Sainfoin CSL 0.269abcd 0.164–0.443 26 1 0
White clover CSL 0.275abcd 0.211–0.359 27 1* 1
Alfalfa CSL 0.281abcd 0.225–0.351 28 2 2
Switchgrass WSG 0.322abcf 0.242–0.429 29 1* 1
Big bluestem WSG 0.322abcd 0.215–0.483 30 0 1
Prairie cordgrass WSG 0.33abcd 0.201–0.542 31 1 0
Japanese clover WSL 0.331abcf 0.242–0.453 32 1* 1
Bird’s–foot trefoil WSL 0.336abe 0.269–0.419 33 2* 2
Indiangrasse WSG 0.34abcd 0.226–0.509 34 0 1
Strawberry clover WSL 0.343abcd 0.242–0.487 35 1 0
Red clover CSL 0.382abe 0.269–0.477 36 1* 1
Alsike clover CSL 0.394abe 0.279–0.523 37 1* 1
Red fescue CSG 0.401abcd 0.240–0.647 38 1 0
Korean clover WSL 0.358a 0.307–0.523 39 1* 2
Crimson clover CSL 0.432abcd 0.263–0.710 40 1 0
Berseem cloverf CSL 0.459ab 0.306–0.689 41 0 1
Buffalograssg WSG 0.468abcd 0.232–0.945 42 0 1
Agroforest Syst
123
Plant responses to decreasing light can range from
linear decreases in forage yield to those that plateau or
peaked under moderate shade as found in Lin et al.
(1999), Semchenko et al. (2012), and our study.
Because net assimilation in C3 plants saturates around
50–60% of maximum sunlight, it is possible plants
grown under moderate shade achieved maximum net
assimilation on most days, while plants grown without
shade absorbed surplus light resulting in high rates of
dark respiration which reduced photosynthetic effi-
ciency. Maximum air temperatures in the non-shade
structures were 0.7 and 1.9 �C higher than under
moderate and dense shade which were covered with
black shade cloth, further increasing dark respiration
rates for plants exposed to full sun. Similar temper-
ature differences among shade structures compared
with the non-shade control was also noted by
Semchenko et al. (2012).
Interactions between shade and year occurred for
five species (Fig. 1) in part due to variable responses in
forage yield from year to year, especially in the non-
shade control. Lower biomass in 2000 was in part
because most species were planted late and harvested
only in the fall of 2000, while in 2001 most species had
2–4 harvests depending on harvest recovery time and
initiation of flowering. Of the 13 perennial forages
screened in 2000 and 2001, only red fescue and alsike
clover showed an interaction between shade treatment
and year, suggesting yield response to shade does not
change as most perennial forages mature from first-
year seedlings to established plants.
Relative distance plasticity index
Forage species that show the least differences in
biomass yield across non-, moderate, and dense shade
(group 1), or at least the latter two treatments (group
5), should in theory have the lowest RDPIs and ought
to be the most shade tolerant species. Among the top
13 species with the lowest RDPIs (Table 3), clustered
fescue, atra paspalum, cheatgrass, orchardgrass,
roundhead lespedeza, eastern gamagrass, and peren-
nial ryegrass are in group 1, while crownvetch, reed
canarygrass, and hoary ticktrefoil are in group 5.
Species with reduced biomass under dense shade
compared to moderate and/or non-shade (groups 2, 3,
and 4) should have higher RDPIs. None of the 12
species in group 2, only bahiagrass out of nine species
in group 3, and smooth brome and panicledleaf
ticktrefoil out of six species in group 4 have low
RDPIs. The calculation of RDPI of smooth brome
(0.136) and panicledleaf ticktrefoid (0.174) included
biomass data from Lin et al. (1999), which showed
smaller differences in biomass than our study across
all three shade levels.
RDPIs confirm relative shade tolerance of reported
observations for several forages. Orchardgrass is
reported to be productive under a wide range of light
Table 3 continued
Species Groupa RDPIb 95% CI Rank Number of cultivarsc
1996–2001 1994–1995
Subterranean clover CSL 0.494abc 0.301–0.811 43 1 0
Prairie dropseed WSG 0.494abc 0.301–0.812 44 1 0
Purple prairie clover WSL 0.567abcd 0.281–1.144 45 1 0
Forb types CSG 0.183B 0.163–0.206 I
WSG 0.252A 0.217–0.292 II
WSL 0.274A 0.242–0.311 III
CSL 0.314A 0.274–0.360 IV
* indicates the number of cultivars of that species shared with Lin et al. (1999)a CSG cool season grasses, WSG warm season grasses, CSL cool season legumes, WSL warm season legumesb RDPIs with the same lower case or upper case letters in the same column are not significantly different (a = 0.05). RDPIs and CIs
are all back transformed from natural log to original scalec Number of cultivars tested in each period of timed–f Forages that are from Lin et al. (1999) but their scientific names do not appear in the text other than this table. sericea lespedeza:
Lespedeza cuneate; Indiangrass: Sorghastrum nutans; berseem clover: Trifolium alexandrinum; buffalograss: Bouteloua dactyloides
Agroforest Syst
123
conditions and is recognized as a shade tolerant
species (Blake et al. 1966; Christie and McElroy
1995). Our RDPI calculated as the average of two
cultivars across several trials (six trials for ‘Bench-
mark’ and three for ‘Justus’) was 0.148, which ranked
orchardgrass as the 6th most shade tolerant out of the
45 species examined. Atra paspalum, a shade tolerant
C4 grass recommended for tropical agroforestry
systems had a low RDPI (0.128), placing it the 2nd
out of 45 species. White clover, reported to be shade
intolerant by Christie and McElroy (1995), has a
relatively high RDPI (0.275) and ranked 27th on the
list of 45 species.
We also assessed the usefulness of RDPI to rank
forage species for shade tolerance by comparing
published relative ranks to our estimated RDPIs.
RDPIs align well with the rankings by Feldhake and
Belesky (2009) for orchardgrass (0.148) being more
shade tolerant than tall fescue (0.226). RDPI and
rankings do not align so well for the shade tolerance
rankings reported by Beard (1965) for red fescue
(0.394) [ perennial ryegrass (0.175) [ tall fescue
(0.226)[Kentucky bluegrass (0.208), or by Kephart
et al. (1992) for tall fescue (0.226)[reed canarygrass
(0.161) [ switchgrass (0.322). RDPIs support the
rankings by Devkota et al. (1997) of orchardgrass
(0.148) being more shade tolerant than perennial
ryegrass (0.175) but not for subterranean clover
(0.494) being more shade tolerant than white clover
(0.275). Discrepancies among relative rankings may
be in part due to measuring different growth responses,
i.e., survival and plant health; amount of root compe-
tition (pasture compared to a few plants in a large pot);
or study duration (a couple months compared to
multiple harvests over an entire growing season). Van
Sambeek et al. (2007) investigated species with widely
differing shade tolerance from multiple screening
trials by comparing the relative changes in forage
yields from plants under moderate and dense shade to
those under non-shade, and then ranked them on a
scale between 0 (least tolerant) and 100% (most
tolerant). There is reasonable agreement between the
reported percentile ranks and RDPIs of our study
except for bahiagrass, Bermudagrass, switchgrass, and
red clover.
C3 and C4 species generally have different degrees
of shade tolerance. Kephart et al. (1992) found that in
response to reduced irradiance, C3 grasses like tall
fescue, reed canarygrass, and deertongue grass
(Dichanthelium clandestinum) have smaller relative
reductions in biomass than C4 grasses such as
switchgrass and big bluestem (Andropogon gerardii),
indicating more shade tolerance within C3 grasses
than C4. This is in agreement with our finding that C3
grasses (cool season) are more resilient to shade
(lower RDPI) in forage yield than C4 grasses (warm
season). However, there was no difference for RDPIs
between legumes (all C3) and C4 grasses.
Conclusion
Multiple screenings evaluating responses of forages to
moderate and dense shade showed most forages did
not change or increased in forage yield, when grown
with adequate water and nutrients in the absence of
root competition from other plants. RDPI that mea-
sures the resilience of a plant to adapt when grown
along an environmental gradient has acceptable con-
cordance with known shade tolerance rankings. Low
RDPIs indicate small changes in yield for forage
species that can adapt to moderate and dense shade.
Several agroforestry systems are characterized by
continuums from moderate to dense shade in the
presence of trees. Our results indicate that for most
forages, yield can be maintained or improved under
moderate shade compared to open grown forages
when tree root competition is minimized. RDPI can be
a useful and convenient indicator for shade tolerance.
Agroforestry practitioners may want to choose forages
with low RDPIs, because these species are more likely
to maintain biomass yield in their agroforestry prac-
tices as trees grow and canopies close.
Acknowledgements This work was funded by the University
of Missouri Center for Agroforestry under cooperative
agreement AG-02100251 with the USDA-ARS Dale Bumpers
Small Farm Research Center, Booneville, AR, and CR
826704-01-0 with the US EPA. We want to express our
appreciation to the HARC staff, especially Steve Kirk for
maintaining the studies in the STSL and harvesting the forages,
Robert McGraw, our retired agronomist, for providing seeds and
guidance, and John Stanovick, a USDA Forest Service
statistician, for helping us on statistical analysis.
References
Abraham EM, Kyriazopoulos AP, Parissi ZM, Kostopoulou P,
Karatassiou M, Anjalanidou K, Katsouta C (2014) Growth,
Agroforest Syst
123
dry matter production, phenotypic plasticity, and nutritive
value of three natural populations of Dactylis glomerata L.
under various shading treatments. Agrofor Syst
88:287–299. doi:10.1007/s10457-014-9682-9
Albaugh JM, Albaugh TJ, Heiderman RR, Leggett Z, Stape JL,
King K, O’Neill KP, King JS (2014) Evaluating changes in
switchgrass physiology, biomass, and light-use efficiency
under artificial shade to estimate yields if intercropped with
Pinus taeda L. Agrofor Syst 88:489–503. doi:10.1007/
s10457-014-9708-3
Beard JB (1965) Factors in the adaption of turfgrass to shade.
Agron J 57:457. doi:10.2134/agronj1965.0002196200570
0050015x
Blake CT, Chamblee DS, Woodhouse WW (1966) Influence of
some environmental and management factors on the per-
sistence of Ladino clover in association with orchardgrass.
Agron J 58:487–489. doi:10.2134/agronj1966.00021962
005800050009x
Callaway R (2007) Positive interactions and interdependence in
plant communities. Springer, Dordrecht
Christie BR, McElroy AR (1995) Orchardgrass. In: Barnes RF,
Miller DA, Nelson CJ (eds) Forages, 5th edn. Iowa State
University Press, Ames, pp 325–334
Devkota NR, Kemp PD, Hodgson J (1997) Screening pasture
species for shade tolerance. Proc Agron Soc NZ
27:119–128
Ehret M, Graß R, Wachendorf M (2015) The effect of shade and
shade material on white clover/perennial ryegrass mixtures
for temperate agroforestry systems. Agrofor Syst
89:557–570. doi:10.1007/s10457-015-9791-0
Feldhake CM, Belesky DP (2009) Photosynthetically active
radiation use efficiency of Dactylis glomerata and Sche-
donorus phoenix along a hardwood tree-induced light
gradient. Agrofor Syst 75:189–196. doi:10.1007/s10457-
008-9175-9
Gaussoin RE, Baltensperger AA, Coffey BN (1988) Response
of 32 bermudagrass clones to reduced light intensity.
HortScience 23:178–179
Gold MA, Garrett HE (2009) Agroforestry nomenclature, con-
cepts, and practices. In: Garrett HE (ed) North American
agroforestry: an integrated science and practice, 2nd edn.
American Society of Agronomy Inc, Madison, pp 45–56
Jiang Y, Duncan RR, Carrow RN (2004) Assessment of low
light tolerance of seashore paspalum and bermudagrass.
Crop Sci 44:587. doi:10.2135/cropsci2004.5870
Kephart KD, Buxton DR, Taylor ES (1992) Growth of C3 and
C4 perennial grasses under reduced irradiance. Crop Sci
32:1033–1038. doi:10.2135/cropsci1992.0011183X00320
0040040x
Lin CH, McGraw RL, George MF, Garrett HE (1999) Shade
effects on forage crops with potential in temperate agro-
forestry practices. Agrofor Syst 44:109–119. doi:10.1023/
A:1006205116354
Loach K (1970) Shade tolerance in tree seedlings. II. Growth
analysis of plants raised under artificial shade. New Phytol
69:273–286. doi:10.1111/j.1469-8137.1970.tb02426.x
Martsolf JD (1966) Microclimatic modification through shade
induced changes in net radiation. Ph.D. Dissertation,
University of Missouri-Columbia
Pearson HA (1983) Forest grazing in the southern United States.
In: Hannaway DB (ed) Proceedings of the international
hilllands symposium foothills for food and forests. Cor-
vallis, OR, USA, pp 247–260
Peri PL, McNeil DL, Moot DJ, Varella AC, Lucas RJ (2002) Net
photosynthetic rate of cocksfoot leaves under continuous
and fluctuating shade conditions in the field. Grass Forage
Sci 57:157–170. doi:10.1046/j.1365-2494.2002.00312.x
Semchenko M, Lepik M, Gotzenberger L, Zobel K (2012)
Positive effect of shade on plant growth: amelioration of
stress or active regulation of growth rate? J Ecol
100:459–466. doi:10.1111/j.1365-2745.2011.01936.x
USDA NRCS (2016) The PLANTS Database. National Plant
Data Team, Greensboro, NC 27401-4901 USA. http://
plants.usda.gov. Accessed 25 April 2016
Valladares F, Niinemets U (2008) Shade tolerance, a key plant
feature of complex nature and consequences. Annu Rev
Ecol Evol Syst 39:237–257. doi:10.1146/annurev.ecolsys.
39.110707.173506
Valladares F, Sanchez-Gomez D, Zavala MA (2006) Quantita-
tive estimation of phenotypic plasticity: bridging the gap
between the evolutionary concept and its ecological
applications. J Ecol 94:1103–1116. doi:10.1111/j.1365-
2745.2006.01176.x
Van Sambeek JW, Navarrete-Tindall NE, Garrett HE, Lin CH,
McGraw RL, Wallace DC (2007) Ranking the shade tol-
erance of forty-five candidate groundcovers for agro-
forestry plantings. Temp Agroforester 15. http://www.nrs.
fs.fed.us/pubs/jrnl/2007/nrs_2007_vansambeek_002.pdf
Varella AC, Moot DJ, Pollock KM, Peri PL, Lucas RJ (2010) Do
light and alfalfa responses to cloth and slatted shade rep-
resent those measured under an agroforestry system?
Agrofor Syst 81:157–173. doi:10.1007/s10457-010-9319-6
Watson VH, Hagedorn C, Knight WE, Pearson HA (1984)
Shade tolerance of grass and legume germplasm for use in
the southern forest range. J Range Manag 37:229–232.
doi:10.2307/3899143
Wong CC, Rahim H, Sharudin MAM (1985a) Shade tolerance
potential of some tropical forages for integration with
plantations. 1. grasses. Mardi Res Bull 13:225–240
Wong CC, Sharudin MAM, Rahim H (1985b) Shade tolerance
potential of some tropical forages for integration with
plantations. 2. legumes. Mardi Res Bull 13:249–269
Yang W, Liu F, Zhou L, Zhang S, An S (2012) Growth and
photosynthetic responses of Canarium pimela and
Nephelium topengii seedlings to a light gradient. Agrofor
Syst 87:507–516. doi:10.1007/s10457-012-9570-0
Agroforest Syst
123